The invention relates to a method and apparatus for detecting optical spectrums.
In principle, a spectrometer for detecting optical spectra consists of a diffraction device, by which an incident beam of the optical radiation that is to be examined is spectrally split, and a detection device which detects the radiation in a spectrally resolved manner. If the optical spectrum is to be detected over a broader spectral region, this usually cannot be accomplished without additional measures. Either individual spectrometers are used for different spectral regions or the different spectral regions are processed differently within the spectrometer.
In a spectrometer disclosed in U.S. Pat. No. 5,638,173, a diffraction device in the form of an optical grating is provided in the beam path of an incident beam. Two splitting filters and one deflection mirror are arranged in the beam path behind the diffraction grating, so that three partial beams are generated. The latter are assigned to three different spectral regions and are detected in a spatially separated manner, in a detector arrangement after passing through a joint spectrometer lens system. Because of the spatial separation of the partial beams, the spectrometer lens system must include large optical components (that is, large lenses) which leads to high weight and costs.
It is also known to provide “nosepieces” with different gratings in spectrometers, so that only one beam path needs be processed in the spectrometer lens system. However, as a result, the different spectral regions can be measured only sequentially (and not simultaneously) and, furthermore, an additional high-precision mechanism is required for changing the gratings.
One object of the present invention, therefore, is to provide a spectrometer which is small and lightweight, and which can process a large spectral region.
Another object of the invention is to provide a method for operating such a system.
These and other objects and advantages are achieved by the method according to the invention for detecting optical spectra, in which two or more partial beams generated from an incident beam and assigned to different spectral regions, travel through a joint spectrometer lens system and are detected in a spatially separated manner. The partial beams generated from the incident beam are directed to respective spatially separated diffraction gratings that are virtually superimposed in the beam path, and are assigned to the different spectral regions. After passing through the diffraction gratings, the partial beams are combined to a joint beam path traveling through the joint spectrometer lens system.
Preferably, the partial beams comprising the different spectral regions are spectrally separated after traveling through the joint spectrometer lens system, and are detected in detectors which are spatially separated and assigned to the different spectral regions.
According to a preferred embodiment of the method of the invention, it is provided that, when they are generated, the partial beams are spectrally separated from the incident beam.
Furthermore, it is preferably provided that the incident beam and the partial beams combined to the joint beam path, travel through the same spectrometer lens system. However, depending on the use, it may be advantageous for technical reasons to use separate spectrometer lens systems: that is, one spectrometer lens system for the incident beam and another one separated therefrom for the partial beams combined to the joint beam path.
According to a particularly preferred embodiment of the method according to the invention, it is provided that three spectrally separated partial beams are generated from the incident beam. The three beams are directed to three diffraction gratings virtually superimposed in the beam path and, after traveling through the joint spectrometer lens system, are detected in three detectors assigned to the respective spectral regions.
Furthermore, the invention also provides an arrangement for detecting optical spectra, which contains a diffraction device arranged in the beam path of an incident beam. A joint spectrometer lens system, is traversed by two or more partial beams which are generated from the incident beam and are assigned to different spectral regions; and a detector arrangement is provided for the spatially separate detection of the partial beams assigned to the different spectral regions. According to the invention, the diffraction device contains spatially separated diffraction gratings, which are assigned to the different spectral regions. A beam splitter device splits the incident beam into the respective partial beams directed to the diffraction gratings, and subsequently combines the partial beams to a joint beam path traveling through the joint spectrometer lens system in the sense of a virtual superimposition of the diffraction gratings.
The detector arrangement preferably contains respective detectors assigned to the different spectral regions. A spectral separating device spectrally separates the partial beams combined in the joint beam path, and directs them to the respective detectors.
According to a preferred embodiment of the invention, the beam splitter device splits the incident beam into the partial beams while spectrally separating them. Furthermore, it is preferably provided that the common spectrometer lens system is arranged in the beam path of the input beam and in the common beam path of the combined partial beams.
In a preferred embodiment of the arrangement according to the invention, the diffraction device contains three diffraction gratings that are virtually superimposed in the beam path, and the detector arrangement contains three detectors assigned to the respective spectral regions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.